This procedure shuts down the mongod instance of a
config server in order to create a
backup of a sharded cluster’s
metadata. The cluster’s config servers store all of the cluster’s
metadata, most importantly the mapping from chunks to
shards.

While one of the three config servers is unavailable,
the cluster cannot split any chunks nor can it migrate chunks
between shards. Your application will be able to write data to the
cluster. See Config Servers for more information.